Composition and process for treating metal surfaces

ABSTRACT

A composition and process for treating metal surfaces that contain at a weight ratio from 1:5,000 to 5,000:1 of at least one metal acetylacetonate selected from the group consisting of Al(C5H7O2)3, V(C5H7O2)3, VO(C5H7O2)2, Zn(C5H7O2)2, and Zr(C5H7O2)4, and at least one compound selected from water-soluble inorganic titanium compounds and water-soluble inorganic zirconium compounds, provides a non-chromate-type composition for imparting an excellent corrosion resistance and paint adherence to the surface of metals, particularly aluminum and its alloys, magnesium and its alloys and zinc and its alloys.

This application claims priority from Japanese patent applications JPH10-307665 filed Oct. 28, 1998 and JP H11-291967 filed Oct. 16, 1999,and International application PCT/US99/23982, filed Oct. 27, 1999.

FIELD OF THE INVENTION

This invention relates to a novel aqueous liquid composition, which isusually hereinafter called a “bath” for brevity, without any implicationthereby that it must be used by immersion only, and to a process fortreating a metal surface. The composition and process can provide thesurfaces of various metals, especially aluminum, aluminum alloys,magnesium, magnesium alloys, and galvanized steel sheet, with anexcellent corrosion resistance and excellent paint adherence.

The baths used to treat aluminum and aluminum alloy surfaces can bebroadly classified into chromate-type baths and non-chromate-type baths.Chromic acid chromate conversion baths and phosphoric acid chromateconversion baths are typical examples of the chromate-type treatmentbaths.

Chromic acid chromate conversion baths first reached practicalapplication in about 1950 and even now are widely used for the surfacetreatment of automotive heat exchangers, aluminum wheels, buildingmaterials, and aerospace materials. The main components in chromic acidchromate conversion baths are chromic acid and a fluoride reactionaccelerator. This type of bath produces a conversion coating containingmoderate amounts of hexavalent chromium on the metal surface.

Phosphoric acid chromate conversion baths originated with the inventiondisclosed in U.S. Pat. No. 2,438,877. The main components in phosphoricacid chromate conversion baths are chromic acid, phosphoric acid, andhydrofluoric acid. A conversion coating whose main component is hydratedchromium phosphate is formed by this type of bath on the metal surface.Since the resulting conversion coating does not contain hexavalentchromium, this type of bath is in wide use at the present time as anunderpaint treatment for the body stock and lid stock of beverage cans.

While the conversion coatings generated by these chromate-type surfacetreatment baths exhibit an excellent corrosion resistance and anexcellent adherence to paint films, these treatment baths also containtoxic hexavalent chromium, and the associated environmental problemshave made it desirable to use treatment baths that are completely freeof hexavalent chromium.

The treatment bath disclosed in Japanese Laid Open (Kokai or Unexamined)Patent Application Number Sho 52-131937 (131,937/1977) is an inventiontypical of the chromium-free non-chromate-type surface treatment baths.This surface treatment bath is an acidic (pH=approximately 1.5 to 4.0)aqueous coating solution that contains phosphate, fluoride, andzirconium or titanium or a mixture thereof. The treatment of metalsurfaces with this surface treatment bath results in the formation onthe metal surface of a conversion coating whose main component is anoxide of zirconium or titanium. This non-chromate-type surface treatmentbath offers the advantage of not containing hexavalent chromium and forthis reason is widely used at present for treating aluminumdrawn-and-ironed, hereinafter usually abbreviated as “DI”, can surfaces.Unfortunately, the coating produced by this non-chromate-type surfacetreatment bath is less corrosion resistant than chromate coatings.

The treatment method disclosed in Japanese Laid Open (Kokai orUnexamined) Patent Application Number Sho 57-41376 (41,376/1982)comprises treating the surface of aluminum, magnesium, or an alloythereof with an aqueous solution containing at least one selection fromtitanium salts and zirconium salts, at least one selection fromimidazole derivatives, and an oxidizer selected from nitric acid,hydrogen peroxide, and potassium permanganate. While the corrosionresistance of the coatings produced by this treatment bath would havebeen considered acceptable 15 years ago, this level of corrosionresistance is not unequivocally satisfactory at the present time.

Japanese Laid Open (Kokai or Unexamined) Patent Application Number Sho56-136978 (136,978/1981) teaches a conversion bath thatcharacteristically comprises an aqueous solution containing a vanadiumcompound and at least one compound selected from the group consisting oftitanium salts, zirconium salts, and zinc salts. However, the conversioncoating formed by this treatment bath cannot be expected to have acorrosion resistance better than or even as good as that of a chromatefilm in the case of challenge by long-term anticorrosion testing.

Thus, as described above, the use of the aforementioned prior-artnon-chromate-type surface treatment baths remains associated withproblems with the corrosion resistance of the produced conversioncoatings. It is for this reason that at present non-chromate-typesurface treatment baths are little used on surface treatment lines wherea particularly good corrosion resistance is required, for example, foraluminum alloy heat exchangers and aluminiferous metal coil and sheetstock.

In summary, then, there has yet to be established a bath for treatingaluminum and aluminum alloy surfaces that does not contain hexavalentchromium, that has an excellent effluent treatability, and that has theability to form highly corrosion-resistant, highly paint-adherentconversion coatings.

For treating magnesium surfaces and magnesium alloy surfaces, chromatetreatments as typified by JIS (Japanese Industrial Standard) H-8651 andMIL M-3171 are in use for treating magnesium and magnesium alloysurfaces. The conversion coatings generated by these chromate-typesurface treatment baths exhibit an excellent corrosion resistance and anexcellent adherence to paint films, but these treatment baths alsocontain highly toxic hexavalent chromium. The associated environmentalproblems have made it desirable to use treatment baths that are entirelyfree of hexavalent chromium.

The process disclosed in Japanese Patent Publication Number Hei 3-6994(6,994/1991) is an invention typical of the chromium-treenon-chromate-type surface treatment baths for magnesium and its alloys.This treatment process comprises a phosphate treatment followed by asilicate treatment and then execution of a silicone treatment after thesilicate treatment. The phosphate treatment coating by itself provides alow level of corrosion resistance and paint adherence when used as anunderpaint treatment for magnesium and magnesium alloy surfaces. Thistreatment method also requires a multistage treatment process, uses hightreatment temperatures, and requires long treatment times.

The known phosphate-based surface treatment methods for magnesium andits alloys include methods that employ treatment baths based on zincphosphate, iron phosphate, calcium phosphate, or zirconium phosphate.However, these methods are not believed to have consistently provided acorrosion resistance that is satisfactory at a practical level.

A manganese phosphate treatment is disclosed in category 7 of JISH-8651. This treatment bath is not acceptable from a practicalstandpoint because it contains chromium, requires high treatmenttemperatures of 80° C. to 90° C., and requires long treatment times of30 to 60 minutes.

Another example of the non-chromate-type technology is found in JapaneseLaid Open (Kokai or Unexamined) Patent Application Number Hei 9-228062(228,062/1997), which teaches a surface treatment process that uses anaqueous solution that contains at least one organometal compoundselected from metal alkoxides, metal acetylacetonates, and metalcarboxylates and at least one film-formation stabilizer orfilm-formation auxiliary selected from acids, bases, their salts, andorganic compounds containing the hydroxyl group, carboxyl group, oramino group. This aqueous solution is applied to magnesium stock at from0 to 50° C. Again, however, the conversion coating formed by thistreatment bath cannot be expected to have a corrosion resistance betterthan or even as good as that of a chromate film in the case of challengeby long-term anticorrosion testing.

Thus, as described above, the use of the aforementioned prior-artnon-chromate-type surface treatment baths for magnesium and its alloysremains associated with problems with the corrosion resistance of theproduced conversion coatings and with requiring treatment conditionsunsuitable from a practical standpoint, i.e., high treatmenttemperatures, long treatment times, and high bath concentrations. It isfor these reasons that at present non-chromate-type surface treatmentbaths are little used on surface treatment lines where a particularlygood corrosion resistance and paint adherence are required, for example,for magnesium alloy automotive materials, aerospace materials, materialsfor electronic devices and instruments, and materials for communicationdevices and instruments.

In summary, then, there has yet to be established a bath for treatingmagnesium and magnesium alloy surfaces that does not contain hexavalentchromium, that has excellent process characteristics, and that has theability to form highly corrosion-resistant, highly paint-adherentconversion coatings.

Chromate treatments and zinc phosphate treatments are the treatmentprocesses generally applied to galvanized materials. The chromatetreatments provide an excellent coating performance, but thecorresponding treatment baths contain toxic chromium and hence raiseissues with regard to the working environment and effluent discharge.The zinc phosphate treatments in some cases are unable to provide anacceptable corrosion resistance.

The non-chromate-type technologies for galvanized materials can beexemplified by the processes disclosed in the following patentdocuments: Japanese Laid Open (Kokai or Unexamined) Patent ApplicationNumber Hei 1-104783 (104,783/1989) discloses a process for producingsurface-treated steel sheet. In this process, steel sheet plated withzinc, aluminum, or a zinc-aluminum alloy is coated with an alcoholsolution containing at least one selection from the alkoxides andacetylacetonates of Si, Ti, Zr, Al, W, Ce, Sn, and Y. An oxide of themetal present in the solution is then formed on the surface of the steelsheet by heating to 200 to 500° C. after application of the bath. Thispreparative method suffers from issues with the working environment andenergy costs, because it must use a flammable alcohol and requiresfairly high temperatures for coating formation.

Thus, just as in the case of aluminum materials and magnesium materials,there has yet to be established a bath for treating the surfaces ofgalvanized materials that does not contain hexavalent chromium, that hasexcellent process characteristics, and that has the ability to formhighly corrosion-resistant, highly paint-adherent conversion coatings.

The present invention is directed to solving the problems describedabove for the prior art. In more specific terms, a major object of thepresent invention is to provide a non-polluting composition and processfor treating surfaces of at least one of aluminum and its alloys,magnesium and its alloys, and steel coated with zinc and its alloys thatcan impart thereto an excellent corrosion resistance and excellent paintadherence.

BRIEF SUMMARY OF THE INVENTION

It has been found that highly corrosion-resistant, highly paint-adherentconversion coatings can be formed on metal surfaces by the use of aspecial surface treatment composition that contains in suitableproportions at least one metal acetylacetonate selected from the groupconsisting of Al(C₅H₇O₂)₃, V(C₅H₇O₂)₃, VO(C₅H₇O₂)₂, Zn(C₅H₇O₂)₂, andZr(C₅H₇O₂)₄, and at least one compound selected from water-solubleinorganic titanium compounds and water-soluble inorganic zirconiumcompounds.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

A composition according to the present invention for treating metalsurfaces comprises, preferably consists essentially of, or morepreferably consists of, water and the following components:

(A) a component of at least one metal acetylacetonate selected from thegroup consisting of Al(C₅H₇O₂)₃, V(C₅H₇O₂)₃, VO(C₅H₇O₂)₂, Zn(C₅H₇O₂)₂,and Zr(C₅H₇O₂)₄; and

(B) a component of at least one compound selected from water-solubleinorganic titanium compounds and water-soluble inorganic zirconiumcompounds, components (A) and (B) being present at a weight ratio of (A)to (B) that is from 1:5,000 to 5,000:1.

A bath according to the present invention for treating metal surfacespreferably, independently for each preference:

has a pH from 2.0 to 7.0;

contains from 0.01 to 50 grams of component (A) as described above perliter of bath, this unit of concentration being freely appliedhereinafter to any constituent of the bath and being usually abbreviatedas “g/l”; and

contains from 0.01 to 50 g/l of component (B) as described above.

A process according to the present invention for treating metal surfacespreferably forms on said metal surface an organic-inorganic compositeconversion coating at a coating weight of 5 to 2,000 milligrams ofcoating per square meter of the surface coated, this unit of coatingweight being hereinafter usually abbreviated as “mg/m²”, by bringing theabove-described bath for treating metal surfaces into contact withaluminum or an alloy thereof, magnesium or an alloy thereof, or zinc oran alloy thereof.

An important feature of the present invention is the formation of anorganic-inorganic composite coating. It is believed that the corrosionresistance of the resulting conversion coating in particular is improvedthrough the formation of this organic-inorganic composite coating.

The water-soluble inorganic titanium compound and/or water-solubleinorganic zirconium compound, which is an essential component in thesurface treatment composition of the present invention, can be one ormore selections, for example, from the sulfates, oxysulfates, nitrates,phosphates, chlorides, ammonium salts, and fluorides of titanium andzirconium. As long as this component is a water-soluble inorganiccompound, its specific type is not critical. However, at least foreconomy, at least one of fluorotitanic and fluorozirconic acids and thesalts of both of these acids are preferred. The water-soluble inorganictitanium and/or zirconium compound(s) are believed to precipitate on thesurface of the metal workpiece as, for example, the oxide, phosphate, orfluoride of Ti or Zr and thus to form a framework or skeletal element ofthe organic-inorganic composite coating that is produced with thesimultaneously precipitating metal acetylacetonate. Moreover, thepresence of the Ti and/or Zr also improves the barrier performance(interception capability) of the coating with respect to corrosiveenvironments and as a result makes possible the formation of a coatingthat has a corrosion resistance and paint adherence superior to the useof only the metal acetylacetonate.

The metal acetylacetonate : water-soluble inorganic compoundconcentration ratio preferably is at least, with increasing preferencein the order given, 1.00:100, 1.00:50, 1.00:10, 1.00:7.0, 1.00:5.0,1.00:3.0, 1.00:2.0, or 1.00:1.40 and independently preferably is notmore than, with increasing preference in the order given, 400:1.00,100:1.00, 10:1.00, 7.0:1.00, 5.0:1.00, or 2.5:1.00. Theorganic-inorganic composite coating formed when this weight ratio isbelow 1:5000 will have a poor corrosion resistance, while production ofthe organic-inorganic composite coating itself becomes difficult atabove 5000:1.

A bath according to the present invention for treating metal surfacesessentially employs water and the hereinabove described surfacetreatment composition. This bath contains the metal acetylacetonatepreferably at from 0.01 to 50 g/l and more preferably at from 0.1, orstill more preferably, 1.0, to 20 g/l. While a conversion coating willbe formed at a metal acetylacetonate content below 0.01 g/l, such acoating will usually have a poor corrosion resistance and paintadherence. Good quality conversion coatings are still formed at above 50g/l, but since no additional increment in performance is obtained above50 g/l, such concentrations are uneconomical due to the additional costof the bath.

The content of water-soluble inorganic titanium compound(s) and/orwater-soluble inorganic zirconium compound(s) is preferably from 0.01 to50 g/l and more preferably from 0.05, or still more preferably 0.5, to10 g/l. While a conversion coating will be formed at a content below0.01 g/l, such a coating will usually have a poor corrosion resistance.Good quality conversion coatings are still formed at above 50 g/l, butsince no additional improvement in performance is obtained above 50 g/l,such concentrations are uneconomical due to the additional cost of thebath.

The pH of a surface treatment bath according to the present inventionmust be within the range from 2.0 to 7.0 and preferably is within therange from 3.0 to 6.0. A pH below 2.0 hinders precipitation of the metalacetylacetonate on the metal surface and can cause irregularities orunevenness in appearance due to excessive etching of the metal surface.Formation of a highly corrosion-resistant conversion coating is stronglyimpaired at a pH above 7.0, and a pH above 7.0 can also cause problemswith bath stability due to a pronounced tendency for the metal ionspresent in the bath to form a precipitate at such pH values. Asnecessary, the pH of the surface treatment bath of the present inventioncan be adjusted into the desiredrange through the use of an acid such asnitric acid, sulfuric acid, phosphoric acid, hydrofluoric acid, orfluorosilicic acid, or a base such as sodium hydroxide, sodiumcarbonate, potassium hydroxide, or ammonium hydroxide.

The stability of the treatment bath can be strongly impaired duringexecution of the surface treatment of the present invention by elutioninto the bath of metal ions, e.g., aluminum, magnesium, or zinc ions,from the metal workpiece. In such cases, an organic acid or alkali metalsalt thereof may be added to the bath as a sequestering agent in orderto chelate the metal ions. Organic acids used for this purpose can beexemplified by gluconic acid, heptogluconic acid, oxalic acid, tartaricacid, organophosphonic acids, and ethylenediaminetetraacetic acid.

An oxidizing agent can also be used in order to accelerate formation ofthe conversion coating of the present invention. This oxidizing agentcan be exemplified by hydrogen peroxide, tungstic acid and its salts,molybdic acid and its salts, permanganic acid and its salts, andwater-soluble organoperoxides such as tert-butyl hydroperoxide((CH₃)₃C—O—OH).

The mass per unit area, usually called “coating weight”, of theorganic-inorganic composite conversion coating formed by the hereinabovedescribed process is preferably from 5 to 2,000 mg/m² and morepreferably is from 50, or still more preferably 140, to 500 mg/m². Thecorrosion resistance and paint adherence may be inadequate at a coatingweight below 5 mg/m². While an excellent corrosion resistance isobtained at coating weights above 2,000 mg/m², no additional incrementin performance is obtained above 2,000 mg/m² and such coating weightsare therefore uneconomical due to the additional cost. Coating weightsabove 2,000 mg/m² are also undesirable because they can cause aconspicuous unevenness in coating appearance and tend to impair thepaint adherence.

In regards to the metal components (Al, V, Zn, Zr, Ti) that mayconstitute the conversion coating, their chemical characteristics in thecoating itself, for example, their bonding status, oxidation state,extent of polymerization or increase in molecular weight, and the like,are not critical.

Highly corrosion-resistant, highly paint-adherent conversion coatingscan be formed by bringing the surface treatment bath of the inventioninto contact with aluminum or an alloy thereof, magnesium or an alloythereof, or zinc or an alloy thereof. This process for treating thesurface of various types of metals will be explained in greater detailin the following.

The surface treatment bath of the invention is used in a preferredembodiment as part of the following process operations:

(1) Surface cleaning/degreasing (this can be acidic, neutral, alkaline,or solvent cleaning/degreasing)

(2) Water rinse

(3) Surface treatment using the surface treatment bath of the presentinvention

(4) Water rinse

(5) Deionized water rinse

(6) Drying.

The surface treatment bath of the present invention is preferablybrought into contact with the metal surface for 1 to 600 seconds at 10,or more preferably 35, to 80° C. The reactivity between the treatmentbath and metal surface usually will be inadequate at contacttemperatures below 10° C., and inadequate reactivity will prevent theformation of good quality conversion coatings. A conversion coating isstill formed at contact temperatures above 80° C., but thecorrespondingly increased energy costs create undesirable economics forsuch temperatures. The extent of reaction will usually be inadequate ata treatment time below 1 second, preventing the formation of a highlycorrosion-resistant conversion coating. At the other end of this range,no additional improvements are seen in the corrosion resistance andpaint adherence of the conversion coating at times in excess of 600seconds. Contact with the surface treatment bath of the invention can beeffected by any means that achieves the required contact, with dippingor spraying being most commonly used.

A surface treatment composition bath according to the invention can beadvantageously applied to pure aluminum and aluminum alloys that containat least 50% by weight of aluminum. The applicable aluminum alloysencompass both multicomponent alloys, e.g., Al—Cu, Al—Mn, Al—Si, Al—Mg,Al—Mg—Si, and Al—Zn—Mg, and metals on which Al plating or Al alloyplating has been executed, for example, Al-plated steel sheet.

The surface treatment composition and bath according to the inventioncan also be advantageously applied to pure magnesium and magnesiumalloys that contain at least 50% by weight of magnesium. Applicablemagnesium alloys encompass multi-component alloys such as Mg—Al—Zn,Mg—Zn, and Mg—Al—Zn—Mn, and the magnesium or alloys can be plated onother metals.

Zinc and zinc alloys to which the invention can be advantageouslyapplied include in particular metals on which Zn plating has beenexecuted, including hot-dip zinc-plated steel sheet, galvannealedhot-dip zinc-plated steel sheet, Al/Zn alloy-plated steel sheet (Galfan™and Galvalume™), electrogalvanized steel sheet, and alloyelectrogalvanized steel sheet.

Such factors as the shape and dimensions of the metallic substrate towhich the invention is applied are not critical, and, for example, theinvention encompasses the treatment of sheet stock and various types ofmoldings. The surface of the workpiece may be in any condition as longas a metal as described above is present at least at a portion of thesurface. For example, the surface can be cold rolled or plated as such,or can have been subjected to a treatment such as shot blasting,roughening with acid or alkali, or activation.

The effects of the composition, bath, and process of the invention areillustrated more specifically below through working and comparativeexamples.

EXAMPLES 1 TO 5 Comparative Examples 1 to 4

The following sample substrate materials were used in these examples:

Al—Mn alloy sheets according to Japanese Industrial Standard (“JIS”)3004, with dimensions of 150 millimeters (hereinafter usuallyabbreviated as “mm”)×70 mm×0.2 mm thick;

Die-cast sheets with dimensions of 150 mm×100 mm×1 mm thick of AZ91Dmagnesium alloy as specified by JIS H2222; and

Galvannealed hot-dip zinc-plated steel sheets with dimensions of 150mm×70 mm×0.8 mm thick.

Process Conditions

The surface-treated samples were prepared by treatment according to thefollowing operations in the sequence (1)→(2)→(3)→(4)→(5)→(6).

(1) Degreasing (43° C., 2 minutes, dipping), using an aqueous solutionof 2% FINECLEANER® L4460A and 1.2% FINECLEANER® L4460B (both commercialproducts of Nihon Parkerizing Co., Ltd.).

(2) Tap water rinse (ambient temperature, 30 seconds, spray).

(3) Surface treatment (dipping) as detailed in the tables below.

(4) Tap water rinse (ambient temperature, 30 seconds, spray).

(5) Deionized water rinse (ambient temperature, 30 seconds, spray).

(6) Drying (80° C. for 3 minutes in a forced convection oven).

(“Ambient temperature” means temperature as normally maintained inbuildings for human comfort, i.e., about 18-23° C.)

The metal acetylacetonates used are listed below in Table 1, thewater-soluble titanium compounds used are listed below in Table 2, thewater-soluble zirconium compounds used are listed below in Table 3, andthe reagents used to adjust the pH of the surface treatment baths arelisted below in Table 4, in each instance together with the identifyingsymbols used for them in later tables.

TABLE 1 Identifying Acetylacetonate Source Name and Chemical FormulaSymbol Aluminum acetylacetonate Al(C₅H₇O₂)₃ a Vanadium acetylacetonateV(C₅H₇O₂)₃ b Vanadyl acetylacetonate VO(C₅H₇O₂)₂ c Zinc acetylacetonateZn(C₅H₇O₂)₂ d Zirconium acetylacetonate Zr(C₅H₇O₂)₄ e

TABLE 2 Identifying Titanium Source Name and Chemical Formula Symbol 40%Solution in water of fluorotitanic acid H₂TiF₆ A 20% Solution in waterof titanium sulfate Ti(SO₄)₂ B

TABLE 3 Identifying Zirconium Source Name and Chemical Formula Symbol20% Solution in water of fluorozirconic acid H₂ZrF₆ a Ammoniumfluorozirconate (NR₄)₂ZrF₆ b

TABLE 4 Identifying pH Adjustment Agent Name and Chemical Formula Symbol67.5% Solution of nitric acid in water HNO₃ a 40% Solution offluorosilicic acid in water H₂SiF₆ b 25% Solution in water of ammoniaNH₄OH c

Surface treatment was performed using the treatment conditions andsurface treatment bath compositions reported in Tables 5 and 6. Theamounts of the reagents reported in the treatment bath compositioncolumns in Tables 5 and 6 are values calculated for the pure reagent.The surface treatment conditions used in Comparative Examples 5 to 9 arereported further below.

Comparative Example 1 used a metal acetylacetonate as the only componentof the treatment bath in order to provide a comparative example testingthe formation of a coating of the metal acetylacetonate alone.Comparative Example 2 used a water-soluble titanium compound as the onlycomponent of the treatment bath in order to provide a comparativeexample testing the formation of a coating of the inorganic titaniumcompound alone. Comparative Example 3 employed a treatment bathcomprising both the water-soluble inorganic titanium compound and thewater-soluble inorganic zirconium compound in order to provide acomparative example testing the formation of an inorganic compositecoating constituted of titanium and zirconium but lacking the metalacetylacetonate. Comparative Example 4 was directed to the formation ofcoatings with very low coating weights.

In Comparative Example 5, a 2% solution in water of a commercialzirconium phosphate surface treatment agent (ALODINE® 4040 from NihonParkerizing Co., Ltd.) was used to carry out surface treatment. Thissolution was applied to the above-described Al alloy sheet by sprayingfor 60 seconds at 50° C., after which the corrosion resistance and paintadherence were evaluated.

In Comparative Example 6, an aqueous solution of a commercial phosphoricacid chromate surface treatment agent (mixed aqueous solution of 4% ofALCHROM® K702SL and 0.3% of ALCHROM® K702AC, both from Nihon ParkerizingCo., Ltd.) was used to carry out surface treatment. This solution wasapplied to the above-described Al alloy sheet by spraying for 20 secondsat 50° C., after which the corrosion resistance and paint adherence wereevaluated.

TABLE 5 Part A Active Ingredients and Their Concentrations in g/l in theSurface Treatment Bath for This Example Treatment Conditions pH ContactExample Metal Titanium Zirconium Adjustment Temperature, Time, NumberAcetylacetonate Source Source Agent pH ° C. Seconds 1 e 1.2 A 0.5 NoneNone None 3.0 60 120  2 b 0.1 None None a 1.5 c 5.8 35 300  c 1.0 3 d20.0  B 10.0  b 1.0 b 2.7 70  3 4 a 1.0 None None a 3.0 c 4.6 50 90 5 a0.5 A 1.0 a 1.0 a 3.8 70 60 d 4.0 Part B Example Coating Weight, SaltSpray Corrosion Adherence, % of Grid Number Substrate mg/m² ResistanceRating Squares Remaining 1 Al alloy 290 ++ 100 Mg alloy 615 ++  99 Znplating 190 + 100 2 Al alloy 400 ++ 100 Mg alloy 1300  ++ 100 Zn plating360 ++  99 3 Al alloy 185 + 100 Mg alloy 680 ++  98 Zn plating 190 +  984 Al alloy 200 +  99 Mg alloy 420 ++ 100 Zn plating 140 +  98 5 Al alloy780 ++ 100 Mg alloy 1850  ++  98 Zn plating 1120  ++  99

TABLE 6 Part A Active Ingredients and Their Concentrations in g/l in theSurface Treatment Bath for This Comparative Example Treatment ConditionsComparative pH Contact Example Metal Titanium Zirconium AdjustmentTemperature, Time, Number Acetylacetonate Source Source Agent pH ° C.Seconds 1 a 1.0  None None None None b and c 4.6 50 90 2 None None A5.0  None None c 3.0 40 30 3 None None A 1.0  a 1.0 c 3.8 70 60 4 e0.005 A 0.005 None None c 5.5 20  2 5 None None None None None NoneNone * 50 60 6 None None None None None None None * 50 20 7 None NoneNone None None None None * 40 60 8 None None None None None None None *95 1800  9 None None None None None None None * 43 120  Part BComparative Example Coating Weight, Salt Spray Corrosion Adherence, % ofGrid Number Substrate mg/m² Resistance Rating Squares Remaining 1 Alalloy 175 x 98 Mg alloy 350 Δ 98 Zn plating 110 x 98 2 Al alloy 185 x 96Mg alloy 240 x 94 Zn plating 120 x 91 3 Al alloy 400 Δ 96 Mg alloy 630 Δ95 Zn plating 190 x 90 4 Al alloy  1 x 72 Mg alloy  2 x 85 Zn plating  1x 79 5 Al alloy 100 x 100  6 Al alloy Cr: 70  + 100  7 Al alloy Cr: 170++ 99 Mg alloy Cr: 50  + 99 Zn plating Cr: 70  ++ 100  8 Mg alloy Cr:800 ++ 100  9 Zn plating 4000  x 91 *The pH value for these baths wasnot reported.

In Comparative Example 7, a 7% solution in water of a commercial chromicacid chromate surface treatment agent (ALCHROM® 713M from NihonParkerizing Co., Ltd.) was used to carry out surface treatment. Thissolution was applied to the above-described Al alloy sheet, Mg alloysheet, and Zn-plated steel sheet by dipping for 60 seconds at 40° C.,after which the corrosion resistance and paint adherence were evaluated.

In Comparative Example 8, a treatment bath based on MIL-M-3171C (TYPEIII, with a main component of sodium bichromate) was used for surfacetreatment. This bath was applied to the Mg alloy sheet by dipping for 30minutes at 95° C., after which the corrosion resistance and paintadherence were evaluated.

In Comparative Example 9, after degreasing (1) and water rinsing (2) theworkpiece was dipped for 30 seconds at 25° C. in a 0.1% aqueous solutionof a commercial titanium-based surface conditioner (PREPALENE® 4040 fromNihon Parkerizing Co., Ltd.). This was followed by surface treatmentwith an aqueous solution of a commercial zinc phosphate-based surfacetreatment agent (mixed aqueous solution of 5% of PALBOND® L3020, 0.5% ofAdditive 4813, 2% of Additive 4856, and 1% of Neutralizer 4055, all fromNihon Parkerizing Co., Ltd.). This bath was applied to the Zn-platedsteel sheet by dipping for 120 seconds at 43° C., after which thecorrosion resistance and paint adherence were evaluated.

Evaluation Methods

(1) Coating Weight: The coating weight of the entire organic-inorganiccomposite coating was measured using either a fluorescence x-rayanalyzer or stripping by dipping for 5 minutes at 90° C. in 5 weight %aqueous chromic acid solution.

(2) Corrosion Resistance: The corrosion resistance was evaluated usingthe salt spray test described in JIS Z-2371. The extent of corrosiondevelopment on the surface-treated sheet was evaluated visually afterthe salt spray test and reported on the following scale:

++=area of corrosion less than 10%;

+=area of corrosion at least 10%, but less than 30%;

Δ=area of corrosion at least 30%, but less than 50%;

×=area of corrosion at least 50%.

The salt spray times for each of the surface-treated samples were:

For Al alloy sheet 480 hours For Mg alloy sheet  24 hours For Zn-platedsteel sheet 120 hours

(3) Paint Adherence: Paint adherence testing was carried out on the Alalloy sheet, Mg alloy sheet, and Zn-plated steel sheet samples aftersurface treatment under the conditions of Examples 1 to 5 andComparative Examples 1 to 9. The surface of the sample was coated to adry film thickness of 10 micrometres (hereinafter usually abbreviated as“μm”) with an epoxy resin paint from Kansai Paint Co., Ltd. and thesample was then baked for 10 minutes at 200° C. A grid of 100 squares(width=2 mm) was subsequently introduced in the center of the paintedsheet using a cutter, after which the sample was dipped for 60 minutesin boiling deionized water. After this boiling water challenge, thepainted sheet was air-dried and then subjected to a peeling test withcellophane tape. The paint adherence was evaluated on the basis of thenumber of grid squares that were not peeled off.

In this test, a larger number of remaining grid squares is indicative ofa better paint adherence. A score of 98 or better indicates asatisfactory performance at the level of practical application.

The results of the evaluations are reported in Tables 5 and 6. Theseresults demonstrate that the conversion coatings formed by the surfacetreatment baths of the present invention have a corrosion resistance andpaint adherence equal to that of conventional chromate coatings.Moreover, the results in these tables demonstrate that an excellentcorrosion resistance can be realized by the formation at appropriatecoating weights of organic-inorganic composite coatings that containboth metal acetylacetonate and at least one of titanium and zirconium.

What is claimed is:
 1. A process for forming a corrosion reducingcoating over a surface selected from the group consisting of aluminumand alloys thereof, magnesium and alloys thereof, and zinc and alloysthereof by coating said surface with an aqueous liquid compositioncomprising water and the following components: (A) a component of atleast one metal acetylacetonate selected from the group consisting ofAl(C₅H₇O₂)₃, V(C₅H₇O₂)₃, VO(C₅H₇O₂)₂, and Zn(C₅H₇O₂)₂; (B) a componentof at least one compound selected from water-soluble inorganic titaniumcompounds and water-soluble inorganic zirconium compounds, components(A) and (B) being present at a weight ratio of (A) to (B) that is from1:5.000 to 5,000:1 to form a coating having a mass per unit area that isfrom 5 to 2,000 mg/m².
 2. A process according to claim 1 wherein saidsurface is contacted with an aqueous liquid composition which has a pHvalue from 2.0 to 7.0; a concentration of component (A) that is from0.01 to 50 g/l; a concentration of component (B) that is from 0.01 to 50g/l; and a weight ratio of (A) to (B) is from 1,00:100 to 400:1.00.
 3. Aprocess according to claim 1 wherein said surface is contacted with anaqueous liquid composition which has a pH value from 3.0 to 6.0; aconcentration of component (A) that is from 0.1 to 20 g/l; aconcentration of component (B) that is from 0.05 to 10 g/l; and a weightratio of (A) to (B) is from 1.00:10 to 10:1.00.
 4. A process accordingto claim 1 wherein said surface is contacted with an aqueous liquidcomposition which has a pH value from 3.0 to 6.0; a concentration ofcomponent (A) that is from 1.0 to 20 g/l; a concentration of component(B) that is from 0.5 to 10 g/l; and a weight ratio of (A) to (B) is from1.00:5.0 to 5.0:1.00.
 5. A process according to claim 1 wherein saidsurface is contacted with an aqueous liquid composition which has a pHvalue from 3.0 to 6.0; a concentration of component (A) that is from 1.0to 20 g/l; a concentration of component (B) that is from 0.5 to 10 g/l;and a weight ratio of (A) to (B) is from 1.00:5.0 to 5.0:1.00, andwherein component (B) is selected from the group consisting offluorotitanic acid, fluorozirconic acid, and salts of both of theseacids.
 6. A process according to claim 1, wherein during said contactingsaid aqueous liquid composition is maintained at a temperature from 10to 80° C. and contact is maintained for a time that is from 1 to 600seconds.
 7. A process according to claim 6, wherein during saidcontacting said aqueous liquid composition is maintained at atemperature of at least 35° C.
 8. An aqueous liquid composition fortreating a metal surface, said composition comprising water and thefollowing components: (A) a component of at least one metalacetylacetonate selected from the group consisting of Al(C₅H₇O₂)₃,V(C₅H₇O₂)₃, VO(C₅H₇O₂)₂, and Zn(C₅H₇O₂)₂, and (B) a component of atleast one compound selected from water-soluble inorganic titaniumcompounds and water-soluble inorganic zirconium compounds, components(A) and (B) being present at a weight ratio of (A) to (B) that is from1:5,000 to 5,000:1.
 9. An aqueous liquid composition according to claim8, additionally comprising at least one sequestering agent.
 10. Anaqueous liquid composition according to claim 9, wherein at least onesequestering agent is selected from the group consisting of organicacids and alkali metal salts thereof.
 11. An aqueous liquid compositionaccording to claim 8, additionally comprising at least one oxidizingagent.
 12. An aqueous liquid composition according to claim 11, whereinat least one oxidizing agent is selected from the group consisting ofhydrogen peroxide, tungstic acid, salts of tungstic acid, molybdic acid,salts of molybdic acid, permanganic acid, salts of permanganic acid, andwater-soluble organoperoxides.
 13. A aqueous liquid compositionaccording to claim 8, wherein: the composition has a pH value from 2.0to 7.0; there is a concentration of component (A) that is from 0.01 to50 g/l; there is a concentration of component (B) that is from 0.01 to50 g/l; and the weight ratio of (A) to (B) is from 1.00:100 to 400:1.00.14. A aqueous liquid composition according to claim 13, wherein: thecomposition has a pH value from 3.0 to 6.0; there is a concentration ofcomponent (A) that is from 0.1 to 20 g/l; there is a concentration ofcomponent (B) that is from 0.05 to 10 g/l; and the weight ratio of (A)to (B) is from 1.00:10 to 10:1.00.
 15. A aqueous liquid compositionaccording to claim 14, wherein: there is a concentration of component(A) that is from 1.0 to 20 g/l; there is a concentration of component(B) that is from 0.5 to 10 g/l; and the weight ratio of (A) to (B) isfrom 1.00:5.00 to 5.00:1.00.
 16. An aqueous liquid composition accordingto claim 15 wherein component (B) is selected from the group consistingof fluorotitanic acid, fluorozirconic acid, and salts of both of theseacids.
 17. An aqueous liquid composition for treating a metal surface,said composition having a pH value from 3.0 to 6.0 and comprising waterand the following components: (A) 1.0 to 20 g/l of a component of atleast one metal acetylacetonate selected from the group consisting ofAl(C₅H₇O₂)₃, V(C₅H₇O₂)₃, VO(C₅H₇O₂)₂, and Zn(C₅H₇O₂)₂ and (B) 0.5 to 10g/l of a component of at least one water-soluble inorganic compoundselected from the group consisting of titanium sulfates, titaniumoxysulfates, titanium nitrates, titanium phosphates, titanium chlorides,ammonium salts of titanium, titanium fluorides, zirconium sulfates,zirconium oxysulfates, zirconium nitrates, zirconium phosphates,zirconium chlorides, ammonium salts of zirconium, and zirconiumfluorides; wherein the weight ratio of (A) to (B) is from 1.00:10.00 to10.00:1.00.
 18. A method of making an aqueous liquid composition fortreating a metal surface, said method comprising: (i) combining thefollowing components in water to form a solution: (A) a component of atleast one metal acetylacetonate selected from the group consisting ofAl(C₅H₇O₂)₃, V(C₅H₇O₂)₃, VO(C₅H₇O₂)₂, Zn(C₅H₇O₂)₂ and Zr(C₅H₇O₂)₄; (B) acomponent of at least one compound selected from water-soluble inorganictitanium compounds and water-soluble inorganic zirconium compounds;wherein components (A) and (B) are present at a weight ratio of (A) to(B) that is from 1:5,000 to 5,000:1; and (ii) adjusting the pH value ofthe solution to within the range from 2.0 to 7.0 using an acid or abase.
 19. The method of claim 18 wherein the pH value of the solution isadjusted to within the range of 3.0 to 6.0.